class Student {
    String name;
    int age;
    String school;
    String major;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public Student(String name, int age, String school) {
        this.name = name;
        this.age = age;
        this.school = school;
    }

    public Student(String name, int age, String school, String major) {
        this.name = name;
        this.age = age;
        this.school = school;
        this.major = major;
    }

    public void displayInfo() {
        System.out.println("name: " + name);
        System.out.println("age: " + age);
        System.out.println("school: " + (school != null ? school : "未设置"));
        System.out.println("major: " + (major != null ? major : "未设置"));
        System.out.println("------------------------");
    }
}